Miniaturized electronic components such as integrated circuits are typically manufactured using photolithography technology. In a photolithography process, a photoresist layer is formed on a substrate, such as a silicon wafer. The substrate is baked to remove any solvent remained in the photoresist layer. The photoresist is then exposed through a photomask with a desired pattern to a source of actinic radiation. The radiation exposure causes a chemical reaction in the exposed areas of the photoresist and creates a latent image corresponding to the mask pattern in the photoresist layer. The photoresist is next developed in a developer solution, usually an aqueous base solution, to remove either the exposed portions of the photoresist for a positive photoresist or the unexposed portions of the photoresist for a negative photoresist. The patterned photoresist can then be used as a mask for subsequent fabrication processes on the substrate, such as deposition, etching, or ion implantation processes.
One type of photoresist employed in the prior art is a chemically amplified photoresist which uses acid catalysis. Chemically amplified photoresists have increased sensitivity to exposure energy over non-chemically amplified photoresists. A chemically amplified photoresist is especially useful when relatively short wavelength radiation is employed, such as deep UV radiation (150-315 nm wavelengths) and mid-UV radiation (350-450 nm wavelengths).
A typical prior art chemically amplified photoresist, for example, is formulated by dissolving an acid sensitive base polymer and a photoacid generator (PAG) in a casting solution. The base polymer in a chemically amplified positive photoresist typically has acid labile groups bonded to the polymer backbone. When such a photoresist is exposed to radiation, the PAG absorbs photons and produces an acid. The photo generated acid then causes catalytic cleavage of the acid labile groups. A single acid molecule generated in this manner may be capable of cleaving multiple acid labile groups on the base polymer. Thus, fewer photons are needed to render the exposed portion of the photoresist soluble in the developer solution.
Because of the relatively low intensity of a 193 nm laser source and relatively high binding energy of acid labile groups in a 193 nm photoresist, PAGs which can produce stronger Bronsted acid with high sensitivity are preferred to realize such a chemical amplification in commercial 193 nm photolithography. Fluorine-containing PAGs, such as perfluorooctyl sulfonate (PFOS) and perfluoroalkyl sulfonate (PFAS), are generally preferred PAGs in 193 nm photoresist system partially because they result in generation of strong acids.
In recent years, however, there has been a desire in the microelectronics industry to eliminate the use of perfluorinated carbons (PFCs) including PFOS and PFAS due to their detrimental effects on environment, human and animals. Thus, there is a desire to find alternative PAGs which can be used without adversely impacting the performance of lithographic processes. There has also been a desire to minimize or eliminate fluorine content in photoresist in order to improve etch resistance and to improve process latitude in high numeric aperture (NA>0.95) imaging processes. Accordingly, there is a need for new and improved fluorine-free PAGs and chemically amplified photoresist compositions that enable the substantial reduction or avoidance of fluorine content in photoresist compositions.